A federal lawsuit was filed on Wednesday challenging the constitutionality of Mississippi’s law banning adoption by same-sex couples.

According to the Campaign for Southern Equality, Mississippi is the only state left in the nation that bans gay couples from adopting without regard for their qualifications as parents or the best interests of the child.

The case, Campaign for Southern Equality v. Mississippi Department of Human Services, was filed on behalf of four same-sex couples: Kari Lunsford and Tinora Sweeten-Lunsford, who are seeking to adopt a child; Brittany Rowell and Jessica Harbuck, also seeking to adopt; Donna Phillips and Janet Smith, parents to a young daughter; and Kathryn Garner and Susan Hrostowski, who have a 15-year-old son.